1. Field of the Invention
This invention relates generally to measurement devices, and more specifically to an improved flow meter device for measurement of a two-phase flow mixture.
2. Description of the Prior Art
The present invention relates to devices for the measurement of a two-phase flow mixture such, as a liquid and a gas, flowing within a conduit. Such devices are highly beneficial in the measurement of geothermal fluids (where the two phases comprise steam and brine), wet steam, oil and gas, as well as other mixtures containing two or more components. The measurement of two-phase flow is highly desirable or even necessary in the production or processing of fluids. As an example, in the production of geothermal fluids, oil and gas, or the generation and distribution of wet steam used in the stimulation of oil wells, the fluids are either produced from the ground in multiphase components or they are injected into the ground as such. It is highly desirable to know how much of each individual phase component is produced or injected for the management of the production facilities and the underground reservoir.
Unfortunately, the use of conventional single phase measurement techniques encounter problems of separation of phases, pulsation, scaling, plugging, vibration, erosion, unknown density and other conditions which make accurate measurement impossible. Prior art two-phase flow meters all have inherent weaknesses which render these devices very limited in range, accuracy, reliability and/or cost prohibitive. So unsuccessful have been these prior art devices that none have obtained wide-range commercial success. Presently, the measurement of two-phase flow requires the complexity and expense of processing the flow through a large pressure vessel. This large vessel induces the liquid and the vapor to separate into individual components. Each of the individual components can then be measured and tabulated as a subtotal. The cost to install a single metering facility on a geothermal well is approximately $150,000.
Prior art patents such as those to Engdahl (U.S. Pat. No. 2,439,723), Nguyen (4,576,043) and Scott (4,574,643) utilize an orifice. These devices have a restricted operating range. The beta ratio (orifice bore/pipe inside diameter) must be sized to produce a sufficiently strong differential signal. This creates a high pressure loss. Unfortunately, even with judicious sizing, orifices used in two-phase flow encounter noise, pulsation and turbulence interference. The patent to Kuijper (U.S. Pat. No. 4,300,399) teaches an elbow meter used in conjunction with a signal conditioning RMS technique. It requires a high velocity and is limited in range and accuracy. The patent to Huang (4,576,036) utilizes a sampling probe. Representative two-phase sampling is exceedingly complex and is beyond the scope of the present invention. The patent to Jung (4,654,061, and the applicant herein) teaches a device that is not a flow meter but is a geothermal separator. It shows an example of a spin generating element. Cain (4,320,665) shows an ultrasonic device. Pitt (4,144,754) utilizes a gamma ray density meter installed within a loop. Cassell (4,178,801) shows a device that is a separator mounted on top of a power plant boiler. A pressure drop is taken across the full length of the separator and used in conjunction with a steam only measurement taken across a restricted outlet. The liquid is drained back into the boiler.
The patent to Scott (U.S. Pat. No. 4,574,643) teaches a device that is an orifice followed by a helical coil with a shielded pitot-static tube inserted between the ribs of the coil and into the radius. This device is unlike the present invention for the following reasons: Scott utilizes an orifice, while the present invention does not. Scott utilizes a helical coil, while the present invention does not. Scott induces a rotational motion of the total flow, through viscous shear of a vapor, by means of a helical coil. A portion of the flow will be guided by the protuberance of the coil. The centrifugal force generated is weak and dictates a long device. The present invention generates a strong spinning fluid through a direct change in flow direction. Scott does not generate but induces a rotational motion. Scott's device must insert a shielded pitot-static tube within the rotation inducing element. The present invention can be inserted ten or more diameters downstream of the spin generating element. Scott measures a annular vapor flow rate through a partially blocked conduit. The present invention measures an annular vapor rate through a full bore. The Scott device is a long device encompassing approximately seventy-three pipe diameters. The present invention can be less than seven pipe diameters. Finally, the Scott device can encounter a poor signal to noise ratio, acts as a spray nozzle generating small particles which can escape the centrifugal force of the coil, is susceptible to scaling, crevise corrosion, and harmonic failure, is limited to small pipe diameters and must be operated within a restricted range.